Multi-chip modules play an increasingly important role in the electronics industry. Integrated circuit chips within a module may be functionally equivalent, such as an array of memory chips to provide a capability of forty megabytes. Alternatively, the chips may be functionally related, such as a chip set comprising a read only memory chip, a random access memory chip, a microprocessor and an interface chip.
As the number of chips confined within a single module increases, the importance of providing adequate cooling also increases. U.S. Pat. No. 5,006,924 to Frankeny et al., U.S. Pat. No. 5,001,548 to Iversen, U.S. Pat. No. 4,879,629 to Tustaniwskyj et al. and U.S. Pat. No. 4,750,086 to Mittal all describe use of a liquid coolant that is forced to flow through a multi-chip module to absorb thermal energy, whereafter the liquid coolant is removed from the module at an outlet port. Providing a liquid coolant loop through a module is an effective may of ensuring adequate cooling, but is an expensive cooling method. Requiring a mechanism for providing a forced flow of liquid coolant would be cost inefficient in such applications as computer workstations.
For small and medium scale applications in which forced liquid cooling is not a cost-efficient option, heat exchangers, or heat sinks, are used to dissipate thermal energy into the atmosphere surrounding a multi-chip module. Particularly for high power chips that generate a significant amount of thermal energy, this places an importance on the heat transfer interface of the chips to the heat exchanger. Ideally, contact is made between the integrated circuit chips and the structure that begins the thermal path to the surrounding atmosphere. A difficulty with this ideal is that during the fabrication of a manufacturing lot of multi-chip modules, there will be dimensional differences among the modules and even among the various chips within a single module. For example, chips are often encased within a chip carrier before being mounted to a component surface of a substrate that is attached to the heat exchanger. The carriers may have slight differences in height and/or the mounting of the carriers to the substrate may result in slight variations in height or angle with respect to the component surface of the substrate. Various fabrication and machine tolerances are additive, so that the carriers within a multi-chip module will not have coplanar upper surfaces. Bellows assemblies with forced liquid cooling for adaptation to individual chips or carriers of a module, such as described in the Mittal and Tustaniwskyj et al. patents, may be used where cost is not a major concern, but ensuring adequate contact between individual chips and a heat dissipating structure is more difficult in many applications.
Alternatively, thermally conductive pillows may be placed between the heat spreader and the chips, as described in U.S. Pat. No. 5,000,256 to Tousignant, U.S. Pat. No. 4,997,032 to Danielson et al. and U.S. Pat. No. 4,092,697 to Spaight. For example, Spaight describes an electrically nonconductive film contacting a single chip at a first side of the nonconductive film and containing a thermal liquid material at a second side.
It is an object of the present invention to provide a multi-chip module that achieves an adaptive heat transfer interface in a reliable, cost-effective manner. A further object is to provide a multi-chip module that achieves an adaptive heat transfer interface without forcing liquid cooling and that provides an electrical path to semiconductor chips of the module.